The invention relates to a method for joining two components made of a metal material, in particular two components made of metal materials having a clearly different microstructure. The invention also relates to a joined connection of two components made of a metal material.
Numerous joining methods for connecting two components made of metal materials, particularly welding methods, are known from the prior art. In particular, if the materials are made of different metal materials, such as, for example, a forged alloy and a cast alloy, problems arise however in that there can be a relatively abrupt transition of the microstructures, of the moduli of elasticity, of the thermal expansion properties, of the internal stresses as well as of other material-specific characteristic values on the two corresponding joining surfaces of the two components. It is clear that this abrupt transition has had a disadvantageous effect thus far on the strength, testability and formation of internal stress, in particular in the region of the joining surfaces of the joined component.
For this reason, it is already known in principle from the prior art to connect the two components with one other indirectly with the intercession of a third component arranged in between them, wherein the component arranged in between them features transition values with respect to the structure and with respect to strength that lie between those of the components actually being connected. However, this method is extremely laborious, especially since two joined connections are created with possible imperfections.
Therefore, it is the objective of the present invention to create a method for joining as well as a joined connection of two components made of a metal material of the type mentioned at the outset, which can be used to connect the two components to one another in an improved manner.
In order to create a method that can be used to join the two components made of a metal material with one another in a considerably improved manner, the invention provides for at least one of the components to be strengthened and then heat treated in at least a partial region of the joining surface thereof prior to joining. As a result, an abrupt transition of the microstructure, of the modulus of elasticity, of the thermal expansion, of the formation of internal stress or of other characteristic values of the two materials being joined is mitigated in order to thereby achieve an improved connection between the two components made of a metal material and improved testability of the welded seam. The location of the joint and the location of the transition of the material structure are separated by achieving a deep-reaching, exponentially tapering-off microstructure under the corresponding joining surface induced by the strengthening method. As a result, the material pairing is testable and less critical in terms of its strength.
The aforementioned heat treatment is in particular of such a type that it causes a recrystallization. The strengthening can in particular be a deep-reaching strengthening.
The strengthening and subsequent heat treatment can for example be carried out once or several times in succession, and namely, in particular, as a function of the desired structure of the boundary layer structure.
To further refine the core structure of the cast component, the aforementioned method may be used several times in succession.
In a further embodiment of the invention, it has been shown to be particularly advantageous if the corresponding component is strengthened over its entire joining surface prior to joining. Thus, the desired, gradually tapering-off transition between the two partial materials of the components being joined is achieved over the entire joined connection, thereby separating the joining zone and the structural transition. Also considered within the scope of the invention is that both joining surfaces of the two components can be strengthened as the case may be.
In another embodiment of the invention, it has also been shown to be advantageous if the component is provided in the region of at least the strengthened partial region of the joining surface with an exponentially decreasing strengthening. This makes it possible for the desired structural transition to be formed especially advantageously.
It has been shown to be further advantageous if, after the strengthening, the component undergoes a heat treatment in the region of at least the strengthened partial region of the joining surface. This heat treatment can be applied to the entire component or only be carried out locally and close to the surface for example. A desirable microstructure is achieved through the heat treatment in particular in the region of the joint between the two joining surfaces in order to thereby achieve the desired less abrupt transition between the two components.
In this connection, it has been shown to be especially advantageous if the component undergoes a recrystallization by means of the heat treatment in the region of at least the strengthened partial region of the joining surface. This type of recrystallization achieves the desired microstructure in the region of the joint between the joining surfaces of the two components in an especially advantageous manner.
In a further embodiment of the invention, it has also been shown to be advantageous if at least the to-be-strengthened partial region of the joining surface of the one component is strengthened by shot peening, such as ultrasonic shot peening, and/or by surface rolling and/or by drifting and/or by laser shot peening and/or by shock-wave strengthening or by a combination of the strengthening methods. In this case, the advantage of this type of surface peening method is in particular that even with complex components or with complex joining surfaces, it is possible to achieve a deep-reaching strengthening. In addition, these types of surface peening methods are reproducible and very easy to control. It can be beneficial to stress the to-be-strengthened component mechanically and/or thermally simultaneously during strengthening.
As an alternative to this, another embodiment of the invention has shown it to be advantageous if the to-be-strengthened partial region of the joining surface is achieved by surface hardening, in particular in the form of an ultrasonic pulse strengthening. Such a sonopeen method can also be used in a simple manner for extremely complex joining surfaces, wherein an extremely uniform, deep-reaching and exponentially tapering-off strengthening can be achieved.
As an alternative to this, it would also be conceivable for at least the to-be-strengthened partial region of the joining surface to be strengthened by surface rolling. Such a method is extremely quick and cost-effective. However, also considered included in the scope of the invention is that instead of the previously described strengthening methods, other methods can also be used by means of which a strengthening of at least one of the components can be achieved mechanically in a partial region of the joining surface thereof.
The two components made of a metal material can also be connected to one other especially advantageously by a welded connection. In this case, inductive high-frequency pressure welding in particular has been shown to be advantageous, because this makes it possible to achieve an extremely durable and permanent connection of the two components. But other welding methods, such as, for example, friction welding, are conceivable.
The advantages described above in connection with the method according to the invention also apply in a similar manner to the joined connection.
Additional advantages, features and details of the invention are yielded from the following description of a preferred exemplary embodiment as well as on the basis of the drawings.